Chapter 9: Elements of C

Definition: Names used to represent variables, constants, types, functions, and labels in the program.

Rules:

• Max 31 characters (extra ignored).
• First character must be alphabet or underscore (_).
• Cannot use keywords.
• No special symbols allowed except underscore.

Types:

• Standard Identifiers: Special meaning in C (e.g., printf, scanf). Can be redefined (not recommended).
• User-defined Identifiers: Defined by programmer (e.g., marks, salary).

Definition: Words with predefined meaning and purpose. Cannot be redefined. Written in lowercase.

List (32 Keywords): auto, break, case, char, const, continue, default, do, double, else, enum, extern, float, for, goto, if, int, long, register, return, short, signed, sizeof, static, struct, switch, typedef, union, unsigned, void, volatile, while.

Definition: Named memory location to store data. Value can change during execution.

Declaration: Specifying name and type. type variable_name; (e.g., int marks;).

Initialization: Assigning value at declaration. type variable = value; (e.g., int a = 10;).

Garbage Value: Meaningless data in uninitialized variable.

Integer Data Types:

• int: 2 bytes. Range: -32768 to 32767.
• short: 2 bytes. Range: -32768 to 32767.
• unsigned int: 2 bytes. Range: 0 to 65535.
• long: 4 bytes. Range: -2,147,483,648 to 2,147,483,647.
• unsigned long: 4 bytes. Range: 0 to 4,294,967,295.

Floating Point Data Types:

• float: 4 bytes. Range: 10^-38 to 10^38. Precision: 6 decimal places.
• double: 8 bytes. Range: 10^-308 to 10^308. Precision: 15 decimal places.
• long double: 10 bytes. Range: 10^-4932 to 10^4932. Precision: 19 decimal places.

Character Data Type:

• char: 1 byte. Stores ASCII characters. Range: -128 to 127 (signed), 0 to 255 (unsigned).

Definition: Quantity that cannot be changed during execution.

• Integer Constants: Numeric values without decimal (e.g., 10, -5).
• Floating Point Constants: Numeric values with decimal (e.g., 3.14, 2.5e3).
• Character Constants: Single char in single quotes (e.g., 'A', '9').
• String Constants: Characters in double quotes (e.g., "Pakistan").

• Arithmetic: +, -, *, /, % (Modulus - remainder).
• Relational: Compare values. ==, !=, >, <, >=, <=. Returns True (1) or False (0).
• Logical: Combine conditions. && (AND), || (OR), ! (NOT).
• Assignment: = assign value. Compound: +=, -=, *=, /=, %= (e.g., a+=10 same as a=a+10).
• Increment/Decrement: Unary operators. ++ increases by 1, -- decreases by 1.
  • Prefix: ++x (Change then use).
  • Postfix: x++ (Use then change).

Order of evaluation in expression:

1. Parentheses ()
2. Unary !, ++, --
3. Multiplicative *, /, %
4. Additive +, -
5. Relational <, <=, >, >=
6. Equality ==, !=
7. Logical AND &&
8. Logical OR ||
9. Assignment =, +=, etc.